1. Field of the Invention
The present invention generally relates to devices and methods for preparing, in a closed system, a cellular suspension for storage.
2. Description of the Related Art
With recent advances in cell transplantation, tissue engineering and genetic technologies, the living cell is becoming an important therapeutic tool in various medical treatments. The availability and efficacy of medical treatments involving the administration of living cells depends on successful preservation and storage of the living cells.
Cells can remain viable for months or years at cryogenic temperatures (e.g. temperatures below about 173 K). Such cryogenic temperatures are not generally lethal to cells. Instead, cell damage and cell death often occurs when the cells are prepared and cooled. Thus, storage of cells at cryogenic temperatures which are later suitable (viable) for use in medical treatments is possible where the cryogenic temperatures can be obtained without incurring fatal damage to the cells.
The two primary causes of fatal damage to cells during cooling are (1) the formation of ice crystals within the cells, and (2) the loss of water from the interior of the cell by osmosis. If freezing is carried out slowly, ice will tend to form outside the cell rather than inside. With further cooling, water from the interior of the cell will pass by osmosis through the cell membrane to add to the growing extracellular ice crystals. In leaving the cell, large and often fatal concentrations of solutes remain behind in the interior of the cell. Thus, rapid cooling is usually fatal to the cell due to intracellular ice formation; slow cooling is usually fatal due to high concentrations of solute inside the cell.
Various cyroprotectants are often used to avoid the formation of ice and/or delay the onset of ice formation to as low a temperature as possible. Such cryoprotectants known in the art are typically glycerol, dimethylsulfoxide (DMSO), ethylene glycol, propylene glycol, trimethylamine acetate, and other high molecular weight solutes capable of strongly hydrogen-bonding to water. Unfortunately, many cyroprotectants are toxic to cells under certain conditions, e.g. exposure to the cyroprotectant for a certain amount of time at a certain temperature. For example, DSMO is toxic to cells exposed thereto for periods of approximately 30 minutes or more at temperatures above 4° C.
Unfortunately, current devices and methods for the cryopreservation of cells do not allow fast and efficient cryopreservation of multiple cell preparations of uniform concentrations and volumes.